Post on 02-May-2017
Parathyroid Hormones
and Calcitonin Habon, Cecille
Jove, Jessica
Lazo, Kareen
Parathyroid Hormone
• A mechanism for controlling extracellular
calcium and phosphate concentrations by
regulating intestinal reabsorption, renal
excretion, and exchange between the
extracellular fluid and bone of these ions.
Synthesis of PTH
• PTH is translated as a pre-prohormone.
• Cleavage of leader and pro-sequences
yield a biologically active peptide of 84 aa.
• Cleavage of C-terminal end yields a
biologically inactive peptide.
Regulation of PTH
• PTH secretion responds to small alterations in plasma Ca2+ within seconds.
• A unique calcium receptor within the parathyroid cell plasma membrane senses changes in the extracellular fluid concentration of Ca2+.
• This is a typical G-protein coupled receptor that activates phospholipase C and inhibits adenylate cyclase
Regulation of PTH
• When Ca2+ falls, cAMP rises and PTH is secreted.
• 1,25-(OH)2-D inhibits PTH gene expression, providing another level of feedback control of PTH.
Regulation of PTH
Calcium
regulates
PTH
secretion
PTH action
• Increases Calcium and Phosphate
Absorption from the Bone
• Decreases Calcium Excretion and
Increases Phosphate Excretion by the
Kidneys
• Increases Intestinal Absorption of Calcium
and Phosphate
Control of Parathyroid Secretion by Calcium Ion Concentration
• Slightest decrease in Ca++ ion concentration (in ECF)
causes the parathyroid glands to increase their rate of
secretion within minutes
• If a decreased calcium concentration persists, the glands
will hypertrophy, sometimes fivefold or more
• An increase calcium ion concentration (above normal)
cause decreased activity and reduced size of the
parathyroid glands
Conditions:
Excess quantities of calcium in the diet
Increased vitamin D in the diet
Bone absorption caused by factors other than PTH
Calcitonin • 32 amino acid peptide
• Molecular weight: 3400
• Primary stimulus: Increase calcium
concentrations
• Parafollicular cells of the thyroid glands
0.1 per cent of the human thyroid
gland
Remnants of the ultimobrachial glands
of lower animals (such as fish,
amphibians, reptiles, and birds)
• ANTAGOSNIST to PTH
Calcitonin Action
1. Decreases plasma calcium concentration
How to reduce plasma calcium?
Decrease the absorptive activities of the
osteoclasts
Decrease the formation of new
osteoclasts
Increase in osteoblastic activity
Calcitonin Action 2. Has a Weak Effect on Plasma Calcium
Concentration in the Adult Human
Twofolds:
First: Initial reduction of the calcium
ion concentration caused by calcitonin
Second: Daily rates of absorption and
deposition of Calcium [on the bone]
In adults: SLOW
In children: RAPID
Other Calcitonin Actions
• Inhibits resorption (bone)
• Increase secretion of water and
electrolytes (intestine)
• Increase Sodium, Calcium and
phosphate excretion in the urine
(kidneys)
• Decrease gastric acid secretion (GIT)
Hypoparathyroidism • Pathogenesis
– Heavier periods in
females
– Cataracts
– Tingling sensations
– Muscles spasms
– Dry hair and skin;
brittle nails
– Weakened tooth
enamel in kids
• Etiology
– Family History
– Autoimmune Disorder
– Excessive radiation
treatment
– Low levels of Mg in
blood
• Treatment
– Take vitamins with
Calcium and Vitamin D
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Hyperparathyroidism • Primary Hyperparathyroidism
Pathogenesis
– Tumor
– Bone Disease
– Hypercalcemia
– Parathyroid Poisoning and
Metastatic Calcification
– Formation of Kidney Stones
• Secondary
Hyperparathyroidism
Pathogenesis
– Rickets
• Etiology
– Overproduction of
the cells secreting
PTH
– Parathyroid
develops a tumor
• Treatment
– Remove the tumor
surgically
– Acidotic diets and
acidic drugs (for tx
of kidney stones)
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Osteoporosis
• Etiology
– Loss of Calcium
– Too much PTH
• Pathogenesis
– "Thin Bones"
– Malnutrition
– Lack of vitamin C
– Postmenopausal lack of estrogen secretion
– Old age
– Cushing’s syndrome
– Deficiency of protein metabolism
• Treatment
– Remove the bad parathyroid gland
18
Parathyroid Cancer
• Pathogenesis
– Weakness
– Lump in neck
– Trouble swallowing
– Loss of appetite
– Unquenchable thirst
Etiology
Out of control PTH
production
Family history
Hyperparathyroidism
Treatment
Surgery
Radiation therapy
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